Linear Interconnect Networking (LIN) is an industry standard for a single-wire serial communication protocol, based on the common serial communication interface (SCI) (UART) byte-word interface. UART interfaces are now available as a low cost silicon module and are provided as a feature on the majority of micro-controllers. UART interfaces can take many forms, for example they can be implemented in software or as a state machine interface for application specific integrated circuits (ASICs).
LIN is targeted as an easy to use, open, communication standard, designed to provide more reliable vehicle diagnostics. Access to the communication medium in a LIN network is controlled by a master node, so that no arbitration or collision management software or control is required in the slave nodes, thus providing a guarantee of worst-case latency times for signal transmission.
A node in a LIN network does not make use of any information about the system configuration, except for the denomination of the master node. Nodes can be added to the LIN network without requiring hardware or software changes in other slave nodes. The size of a LIN network is typically under twelve nodes, although the LIN network is not generally restricted to twelve nodes. This results from a use of only ‘64’ identifiers together with a relatively low transmission speed of 20 Kbits/sec. The clock synchronization, the simplicity of UART communication, and the single-wire medium are often cited as major factors for the cost efficiency of LIN.
Referring now to FIG. 1, a simplified LIN node 100 is illustrated. FIG. 1 shows the basic block diagram of the LIN physical layer. A digital input, referred to as txd 105, drives the transmit (Tx) LIN bus driver 110. When the digital input txd 105 is at high logic level, the LIN output, on the single communication line LIN communication bus 115, is at a high level, i.e. the supply voltage of the vehicle battery referred to as Vbat.
The signal voltage swing on the single communication LIN bus swings from Vbat to a low level of approximately 1V. The Tx LIN bus driver 110 is supplied by Vbat. Each receiver element in a LIN network comprises a comparator 120, which detects when the voltage signal on the single communication LIN bus crosses a value of 50% of Vbat. The voltage level of the comparator output is therefore controlled by the reference signal 125 input to the comparator 120. When the voltage on the single communication LIN bus is high, i.e. over a level of 50% of Vbat, the receiver logic (rxd) output 130 is at a high (Vbat) logic level.
Referring now to FIG. 2, A LIN network 200 is illustrated. The LIN network 200 comprises one master node (control unit) 205 and one or more slave nodes 220, 230. All nodes include a slave communication task 215, 225, 235 that is divided between a transmit task and a receive task. The master node 205 also includes a transmit task 210 and a receive slave task 215. Communication in an active LIN network is performed on the LIN bus 240 and is always initiated by a master task 210.
Referring now to FIG. 3, the simplified circuit of a node is illustrated. FIG. 3 illustrates the output stage of the Tx bus driver 110. The output stage is connected to Vbat 305 through a diode 310. A resistive load 315 is used as a pull-up function for the output stage, i.e. the single LIN communication bus 115. A typical value for a resistive load 315 of a slave device is 30 Kohm. Thus, the 30 Kohms pull-up resistor is present in each internal LIN node. However, to distinguish the Master node from a slave node a 1 KOhms resistor is placed in series with another diode, and is located outside of the integrated circuit. The transistor 320 functions as a switch, through control of the serial communication interface (SCI) 330, and is therefore able to pull-down the single communication LIN bus 115 to a low level.
However, it has been recognised that when Electro Magnetic Interference (EMI) occurs on the single communication LIN bus 115, via introduction of high frequency component interference, say from a circuit or device operational in the vehicle, the LIN network may fail the Direct Power Injection (DPI) test. In particular, there exists a need to sustain 36 dBm in DPI test (+/−40V on single communication LIN bus 115) with a low transition time between the communication signal transitioning between high and low voltage levels.
Thus, a need exists for an improved LIN network, integrated circuit and method of operation therefor.